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Re: ABNF switch: list rules

From: Julian Reschke <julian.reschke@gmx.de>
Date: Sat, 24 May 2008 10:13:45 +0200
Message-ID: <4837CE39.7080300@gmx.de>
To: Henrik Nordstrom <henrik@henriknordstrom.net>
CC: Bjoern Hoehrmann <derhoermi@gmx.net>, HTTP Working Group <ietf-http-wg@w3.org>

Henrik Nordstrom wrote:
> On fre, 2008-05-23 at 15:19 +0200, Julian Reschke wrote:
> 
>> The more I look into this, the better the original syntax looks :-)
> 
> Yes, there is reasons why HTTP has the list syntax.. and I think that
> one does a great job in keeping the BNF readable.
> 
> The reasons for the implied LWS is the same, to make the grammar more
> readable, but unfortunately that one hasn't worked out very well..
> 
> If we can get the BNF syntax to a level of
> 
>   ABNF + list syntax, without implied LWS
> 
> then a lot is gained.

Right.

In particular it seems it would be wise to solve the "implied LWS" issue 
*first*, and only then start looking at the list production.

> Eleminating the list syntax is mainly a goal to line up the HTTP BNF
> syntax completely with other specifications, but I have a feeling that
> it may be better to extend ABNF with a usable list construct.

I'd prefer that.

If we can't keep it, I'd probably recommend to leave the # notation at 
least in ABNF comments.

> While we are at that topic. The specification probably should make sure
> to recommend producers to not produce lists with empty elements (a
> SHOULD NOT). Not sure we have that in the specs today. Parsers MUST
> accept them however and is what the BNF description describes but there
> quite likely is many broken implementations out there not expecting
> empty elements..

What do others think? Is there consensus for this? In which case we 
should raise a separate issue.

BR, Julian
Received on Saturday, 24 May 2008 08:15:40 GMT

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